figure(3);
S = 1/(1 + P0 * K_opt);
bodemag(S, 'b', gam_opt/WS, 'g');
hold on;
for c=0.8:0.02:1.2
  P = 1/((s-1)*(c*s + 1));
  S_tilde = 1/(1 + P * K_opt);
  bodemag(S_tilde, 'r');
end
bodemag(S, 'b', gam_opt/WS, 'g');
legh = legend('$S$', '$\gamma/WS$', '$\tilde S$', 'Location', 'NorthWest');
set(legh, 'interpreter', 'latex');
title('sensitivity gain for perturbed plant');
